It is already known from the prior art to use also emergency lighting devices in addition to the luminaires to which a mains voltage is supplied. These emergency lighting devices are used in the event of failure of the mains supply in order to ensure a minimum level of illumination in areas in which luminaires to which mains voltage is supplied are installed.
Such emergency lighting devices are capable of monitoring the mains supply voltage and correspondingly establishing an emergency lighting operation as soon as, for example, the mains voltage is below a preset threshold value. Generally, in order to identify the state of the grid, a voltage which is representative of the mains voltage is measured. It is possible, for example, for the mains voltage to be measured directly via an input-side voltage divider. Given knowledge of an emergency state, in particular an excessively low supply voltage, the emergency state of the emergency lighting device is then activated, in which an internal battery or an internal rechargeable battery for supplying power to a lamp is switched on.
Secondly, there are grids in which different prices for the mains supply are demanded at different times. In particular, the current may have a more favorable tariff at night than during the day. In the case of some domestic appliances, the consumer may make use of this tariff system by virtue of switching on certain appliances at night. For example, it is possible to program washing machines or dishwashers such that they are automatically started at night.
Against the background of this prior art, the present invention is now based on the object of improving the operation of light-emitting means with a view to the differentiated tariff system for mains supply.